The present invention relates to systems for the storage, transportation and disposal of used nuclear fuel assemblies.
Used fuel assemblies are a primary byproduct of power-generating nuclear processes, and must generally be stored or disposed of in a manner that limits any impact on the surrounding environment. Temporary storage solutions include the fixation of used fuel assemblies in dry casks, termed dry cask storage. Long term disposal is in many ways preferable to dry cask storage, however, and a number of repository concepts are actively being considered. Many existing dry casks do not satisfy the expected package size limitations for the direct disposal of used nuclear fuel assemblies at the proposed repositories. As a result, used nuclear fuel assemblies may require repackaging into more suitable containers for transportation and/or disposal. However, repackaging used nuclear fuel assemblies creates tremendous radiological, operational and financial liabilities, particularly following an extended storage period.
Currently, storage and transportation are considered separately from disposal under relevant U.S. regulations. For example, the used nuclear fuel management system operates under multiple regulations, e.g., 10 CFR 72 for storage, 10 CFR 50 and 72 for dry cask loading, 10 CFR 71 for transportation, and similar regulations to 10 CFR 60 and 63 for eventual disposal. Existing regulations for storage require the used nuclear fuel to be retrievable. Existing regulations for transportation do not explicitly require that fuel rods be intact or undamaged, and relevant provisions allow for specially designed canisters to move damaged fuel. Transportation regulations currently limit fuel to a maximum burnup of 45 GWd/MTU, primarily based on limited information available on the mechanical properties of high burnup cladding as well as the effects of long-term storage on high burnup (>45 GWd/MTU) fuel. Existing regulations for disposal are specific to the previously planned Yucca Mountain Repository, but are likely to be modified, perhaps substantially, to meet future repository site and geologic media performance objectives, perhaps depending on the geologic media, e.g., clay/shale, salt, or crystalline rock. Because the disposal requirements are currently open-ended and undefined, there is at present no domestic market for dry casks designed to support disposal operations. As a result, storage and transportation casks are being designed, licensed and loaded without regard for disposal operations and requirements.